Add custom 404 page to Tips section of docs

docs/tips.rst

@@ -3,6 +3,32 @@ Tips
 
 Here are some tips about Pelican that you might find useful.
 
+Custom 404 Pages
+================
+
+When a browser requests a resource that the web server cannot find, the web
+server usually displays a generic "File not found" (404) error page that can be
+stark and unsightly. One way to provide an error page that matches the theme
+of your site is to create a custom 404 page, such as this Markdown-formatted
+example::
+
+    Title: Not Found
+    Status: hidden
+    Save_as: 404.html
+
+    The requested item could not be located. Perhaps you might want to check
+    the [Archives](/archives.html)?
+
+The next step is to configure your web server to display this custom page
+instead of its default 404 page. For Nginx, add the following to your
+configuration file's ``location`` block::
+
+    error_page 404 /404.html;
+
+For Apache::
+
+    ErrorDocument 404 /404.html
+
 Publishing to GitHub
 ====================